Vacuum forming is a process by which a plastic sheet is heated and then formed to the shape of a die by applying a vacuum to draw the sheet against the surface of the object. The die must then be withdrawn. Objects suitable for vacuum forming on a unitary rigid die have heretofore been limited to those that do not have undercuts, as an undercut prevents withdrawal of the die from the formed sheet without damage to the formed sheet. Alternatively, a complex, costly die with sliding die portions would be required to allow removal of the sheet.